Human interleukin 13 (hIL13) is a 114 amino acid cytokine secreted by activated T cells. Minty et al. (1993) Nature, 362:248-250; and McKenzie et al. (1993) Proc. Natl. Acad. Sci. USA, 90:3735-3739. hIL13 is involved in regulating several different physiological responses. Among these, hIL13 has been shown to downregulate the production of cytokines involved in inflammation. Minty et al., supra; and de Waal Malefyt et al. (1993) J. Immunol., 151:6370-6381. It has also been shown to upregulate expression of major histo-compatibility class II molecules and CD23 on monocytes, and to regulate various aspects of B cell function De Waal Malefyt et al. (1993) Res. Immunol. 144:629-633; McKenzie et al., supra; and de Waal Malefyt et al. (1993) J. Immunol., 151:6370-6381. In addition to regulating cells of the immune system, IL-13 has also been shown to act on other cell types. For example, IL13 has been shown to modulate expression of vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. Sironi et al. (1994) Blood, 84:1913-1921; Bochner et al. (1995) J. Immunol., 154:799-803; and Schnyder et al. (1996) Blood, 87:4286-4295.
Based on its predicted secondary structure, hIL13 has been added to a growing family of growth hormone-like cytokines that all exhibit bundled aa-helical core topology. Bamborough et al. (1994) Prot. Engin., 7:1077-1082. Structural analyses indicated that hIL13 is a globular protein comprised mainly of four aa-helical regions (helices A, B, C, and D) arranged in a “bundled core.” Miyajima et al. (1992) Ann. Rev. Immunol., 10, 295-331.
While dissimilar at the primary amino acid level, hIL13 and human interleukin 4 (hIL4) bind and signal through a shared receptor complex. Zurawski et al. (1993) EMBO J., 12:2663-2670; and Tony et al. (1994) Eur. J. Biochem., 225:659-66. This shared receptor is a heterodimer that includes a first subunit of approximately 140 kDa termed p140, and a second subunit of approximately 52 kDa termed α′ or IL13Rα1. Idzerda et al. (1990) J. Exp. Med., 173:861-873; Obiri et al. (1995) J. Biol. Chem., 270:8797-8804; Hilton et al. (1996) Proc. Natl. Acad. Sci. USA, 93:497-501; and Miloux et al. (1997) FEBS Letters, 401:163-166. Unlike hIL4, hIL13 does not bind p140 in the absence of α′. Vita et al. (1995) J. Biol. Chem., 270:3512-3517. In addition to the shared receptor, another hIL13 receptor termed the restricted (IL4 independent) receptor exists. In contrast to the shared receptor, the latter receptor binds hIL13 but not hIL4. The restricted receptor is also sometimes called the glioma-associated receptor because it is preferentially expressed at high levels in certain malignant cells, including high grade human gliomas. Debinski et al. (1995) Clin. Cancer Res., 1:1253-1258; and Debinski et al. (1996) J. Biol. Chem., 271, 22428-22433. In addition to being associated with malignancies, hIL13 has also been associated with other pathological conditions. Notably, IL13 has been shown to be involved in pathways that regulate airway inflammation, suggesting that this cytokine might play an important role in asthma and perhaps other allergic pathologies. Webb et al., (2000) J. Immunol. 165:108-113; and Djukanovic, R. (2000) Clin. Exp. Allergy 30 Suppl 1:46-50.